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The evolution of vortices in vertical shear. III: Baroclinic vortices
Author(s) -
Jones Sarah C.
Publication year - 2000
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49712657009
Subject(s) - baroclinity , vortex , vorticity , vortex stretching , horseshoe vortex , barotropic fluid , physics , starting vortex , potential vorticity , mechanics , burgers vortex , geology , positive vorticity advection , classical mechanics , vortex ring
The evolution of baroclinic tropical‐eye lone‐like vortices in environmental vertical shear on an f ‐plane is investigated. Idealized numerical calculations are performed using a primitive‐equation model. The vertical structure of the initial vortex is varied by changing the strength of the upper‐level tangential wind. The baroclinic vortices develop a vertical tilt and a cyclonic rotation of the mid‐level centre about the surface centre occurs. In most of the calculations the upper‐level part of the vortex is advected away from the surface centre. The motion of the upper‐level part of the vortex can be attributed to advection by the flow associated with large‐scale asymmetries in the potential vorticity and to the vertically penetrating flow associated with the potential vorticity of the lower portion of the tilted vortex. As in the case of initially barotropic vortices the cyclonic rotation is found to depend on the parameters in the Rossby penetration depth. The height at which the environmental flow is equal to the Speed of vortex motion is found to be higher for vortices with stronger flow at upper levels. This is consistent with observations of tropical cyclones. Significant changes in the potential‐vorticity structure of the vortex occur, especially at upper levels. The vortex becomes elliptic in shape and may extrude filaments of potential vorticily. These filaments thin, and sometimes break away from the main vortex, which as a result becomes more symmetric. The separation of the filaments from the main part of the vortex is often accompanied by a decrease in the vortex tilt. A: some levels no filaments form and the elliptic vortex becomes more symmetric with time. Calculations with a barotropic model show that both the potential‐vorticity structure of the initial vortex, and the horizontally sheared flow associated with the vertical projection of the tilted potential‐vorticity anomaly, play a role in the changes in the vortex Structure. The development of potential‐temperature asymmetries and an adiabatic vertical circulation are shown to be related to the direction of the vortex tilt. This occurs even when the direction of tilt changes with height. The changes in the low‐level static stability associated with the vortex tilt are investigated and the implications for tropical‐cyclone intensity change are discussed.